Cisco CCNP and CCIE Study Notes

The following routers are connected back-to-back with ISDN PRI network-side simulation configured on one end. With the configuration shown below, pings to the far end IP addresses fail. However if the dialer2 interface is unconfigured from both routers, then the call comes up and the other end can be pinged. The same is true if the dialer1 interface is removed from both routers. If both dialer interfaces are configured as below on both routers, then no pings succeed and calls do not come up.

What is the problem here and how can it be fixed?

Router1

isdn switch-type primary-5ess
!
controller T1 4
 framing esf
 linecode ami
 pri-group timeslots 1-24
!
interface Serial4/0:23
 no ip address
 dialer pool-member 1
 isdn switch-type primary-5ess
 isdn protocol-emulate network
 no cdp enable
!
interface Dialer1
 ip address 10.10.10.1 255.255.255.0
 encapsulation ppp
 dialer pool 1
 dialer string 2222222
 dialer-group 1
!
interface Dialer2
 ip address 20.20.20.1 255.255.255.0
 encapsulation ppp
 dialer pool 1
 dialer string 222
 dialer-group 1
!
dialer-list 1 protocol ip permit

Router2

isdn switch-type primary-5ess
!
controller T1 4
 framing esf
 linecode ami
 pri-group timeslots 1-24
!
interface Serial4/0:23
 no ip address
 dialer pool-member 1
 isdn switch-type primary-5ess
 no cdp enable
!
interface Dialer1
 ip address 10.10.10.2 255.255.255.0
 encapsulation ppp
 dialer pool 1
 dialer string 1111111
 dialer-group 1
!
interface Dialer2
 ip address 20.20.20.2 255.255.255.0
 encapsulation ppp
 dialer pool 1
 dialer string 111
 dialer-group 1
!
dialer-list 1 protocol ip permit

Consider the configuration used for multilink PPP a couple of blog posts ago. With that configuration the IP routing table looks like the following

R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
     D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
     N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
     E1 - OSPF external type 1, E2 - OSPF external type 2
     i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
     * - candidate default, U - per-user static route, o - ODR
     P - periodic downloaded static route

Gateway of last resort is not set

   10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       10.10.10.2/32 is directly connected, Multilink1
C       10.10.10.0/24 is directly connected, Multilink1

Note how there is a host route to the IP address at the far end of the multilink PPP connection. What do you need to configure to eliminate this host route that is installed by default when multilink PPP is configured?